1. Field of the Invention
The invention relates to a lens assembly having a plurality of optical members and a barrel into which the plurality of optical members are mounted, and to an imaging apparatus having the lens assembly.
2. Description of the Related Art
A lens assembly having a plurality of optical members and a barrel into which the plurality of optical members are mounted has been known.
FIG. 12 is a view illustrating a section of a related-art lens assembly, in which the section includes an optical axis of a taking lens. FIG. 13 is an enlarged sectional view illustrating a part of the lens assembly shown in FIG. 12, in which the taking lens, a spacer ring, and the barrel are in close contact with each other.
FIG. 12 shows the lens assembly 100 including a taking lens 101 of a first group, a taking lens 102 of a second group, and a taking lens 103 of a third group in order from the incident side of subject light A. Between the taking lens 102 of the second group and the taking lens 103 of the third group, a spacer ring 104 configured to regulate a space between these taking lenses 102 and 103 of the second and third groups is disposed. Furthermore, FIG. 11 shows a barrel 105 into which the taking lenses 101, 102, and 103 of the first to third groups and the spacer ring 104 are mounted, and an O-ring 106 that is disposed between the taking lens 101 of the first group and the barrel 105.
Specifically, as shown in FIG. 13, the taking lens 101 of the first group has an outer peripheral surface 101a, and the barrel 105 has an inner surface 105a. The O-ring 106 is fitted onto the outer peripheral surface 101a, and is disposed in a state where the O-ring is pressed by the outer peripheral surface 101a and the inner surface 105a. The O-ring 106 is a member made of rubber that exhibits waterproof performance after the taking lens 101 of the first group is mounted into the barrel 105.
Furthermore, the taking lens 102 of the second group has an outer peripheral surface 102a, and the barrel 105 has an inner surface 105b. The taking lens 102 of the second group is mounted in a state where the outer peripheral surface 102a of the taking lens 102 of the second group is in close contact with the inner surface 105b of the barrel 105. Further, the spacer ring 104 has an outer peripheral surface 104a, and the barrel 105 has an inner surface 105c. The spacer ring 104 is mounted in a state where the outer peripheral surface 104a of the spacer ring 104 is in close contact with the inner surface 105c of the barrel 105. Moreover, the taking lens 103 of the third group has an outer peripheral surface 103a, and the barrel 105 has an inner surface 105d. The taking lens 103 of the third group is mounted in a state where the outer peripheral surface 103a of the taking lens 103 of the third group is in close contact with the inner surface 105d of the barrel 105. In addition, the taking lens 103 of the third group is mounted in a state where an annular area 103b that is a periphery of the image-side surface of the taking lens 103 of the third group is also in close contact with a surface 105e of the barrel 105.
When the lens assembly 100 is assembled, first, the taking lens 103 of the third group is mounted into the barrel 105. Then, the spacer ring 104 is mounted into the barrel 105, and additionally the taking lens 102 of the second group is mounted into the barrel 105. Then, the O-ring 106 is fitted onto the outer peripheral surface 101a of the taking lens 101 of the first group, and finally the taking lens 101 of the first group is mounted into the barrel 105. In such a manner, the lens assembly 100 configured to secure close contact between the outer peripheral surface 101a of the taking lens 101 of the first group and the O-ring 106 and close contact between the inner surface 105a of the barrel 105 and the O-ring 106 is assembled.
JP 2002-90603 A (corresponding to U.S. Pat. No. 6,507,700) has proposed a technique that caulks a protrusion of a leading end of a barrel on a front surface side of a taking lens in the way of thermal adhesion in a state where an O-ring disposed between an outer peripheral surface of the taking lens and an inner surface of the barrel is pressed.
As described above, when the lens assembly is assembled, first, the taking lens of the third group is mounted into the barrel. Next, the spacer ring is mounted into the barrel, and additionally the taking lens of the second group is mounted into the barrel. Finally, the taking lens of the first group having the O-ring fitted thereto is mounted into the barrel. Here, in a state where the taking lens of the third group, the spacer ring, and the taking lens of the second group are sequentially mounted into the barrel, the taking lens of the first group having the O-ring fitted thereto is mounted into the barrel. In this case, outer peripheral surfaces of the taking lens of the third group, the spacer ring, and the taking lens of the second group, which have already mounted into the barrel, are in close contact with the respective inner surfaces of the barrel. Thus, air in the barrel is pressed by the taking lens of the first group, and thereby the air is compressed. Then, the pressed air pushes back on the taking lens of the first group in an opposite direction (a direction toward the object side of the barrel) to a direction in which the taking lens is mounted. Hence, in the related-art lens assembly, there is a problem in that assembling workability is poor.